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<p>Free (or open source) software is software that comes with a license that gives users certain rights. In particular the right to use the software, to modify it, to obtain its source, and to pass it on (under the same terms). Notice that the term &quot;free&quot; is about rights, not money. The Free Software Foundation (creators of the GNU GPL) speaks of free in this context as in &quot;free speech&quot;, not as in &quot;no cost&quot;.</p>
<p>Trolltech supports the free software concept by providing the Qt Open Source Edition. You can use this edition of Qt to create free software, i.e&#x2e; software that is licensed under the GNU GPL or a similarly recognized open source license. Trolltech's support of open source with the Qt Open Source Edition has enabled large successful software projects like KDE to thrive, with thousands of developers around the world using Qt Open Source Edition at no cost to themselves. With the release of Qt 4, Qt Open Source Edition is available for Unix/X11, Mac OS X, and Windows.</p>
<p>The Open Source Edition can be downloaded from <a href="http://www.trolltech.com/developer/downloads">Trolltech's website</a>.</p>
<p>It is also possible to develop commercial software using Qt: but to do so you must buy a commercial license for one of the <a href="commercialeditions.html">Qt Commercial Editions</a>. If you buy a commercial edition of Qt you can sell your software for any price and with any license you like. Thousands of commercial companies use the commercial edition of Qt to develop the products they sell.</p>
<p>If you use the Qt Open Source Edition, there are certain licensing conditions that the GNU GPL imposes on you, to ensure that your users enjoy the freedoms guaranteed by the GPL. Users are entitled to:</p>
<ol type="1">
<li>Run your software for any purpose.</li>
<li>Obtain and study your software's source code, and adapt it to their needs.</li>
<li>Redistribute your software and its source code to others (under the same terms).</li>
<li>Improve or modify your software, and release these changes to the public.</li>
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<p>These freedoms apply to all the source code for all the modules your software is based on, regardless of whether they have been written by you or by others. The freedoms also apply to any associated interface definition files, and even include the scripts and control files used to control compilation and installation of the executable; otherwise users could not exercise their rights.</p>
<p>This means that you cannot use a Qt Open Source Edition if your software must be built with any modules that impose conditions on you that contradict the conditions of the GNU GPL, including, but not limited to, software patents, commercial license agreements, copyrighted interface definitions or any sort of non-disclosure agreement. In these circumstances you must use a commercial edition of Qt.</p>
<p>See the <a href="http://www.trolltech.com/developer/faqs/Licensing">License FAQ</a> for answers to frequently asked questions on Qt Open Source Edition licensing and its implications.</p>
<p>More information on Free and Open Source software is available online:</p>
<ul>
<li>GNU GPL: <a href="http://www.gnu.org/">http://www.gnu.org/</a>.</li>
<li>Open Source licensing: <a href="http://www.opensource.org/">http://www.opensource.org/</a>.</li>
</ul>
<p>Information about Qt Commercial License Agreements is available in the <a href="http://www.trolltech.com/products/qt/licenses/licensing/">Qt Licensing Overview</a> on Trolltech's web site or by email from <a href="mailto:sales@trolltech.com">sales@trolltech.com</a>.</p>
<p>If you are in doubt what edition of Qt is right for your project, please contact <a href="mailto:info@trolltech.com">info@trolltech.com</a>.</p>
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